1. Field of the Invention
The present invention relates to an engine control apparatus for continuing the cooling of an engine following the shutting off of the engine's ignition switch or other actuating mechanism. The invention is particularly applicable to controlling the operation of turbo-charger equipped vehicle engines so as to minimize the risk of engine and bearing damage from overheating.
2. Description of the Prior Art
During operation, vehicle engines generate significant amounts of heat. This heat is commonly dissipated by coolant, such as lubricating oil circulating through the engine and components. Alternately, cooling is frequently accomplished by air or other fluid circulating through a heat exchanger in heat exchange relationship with the engine and components. These engines are turned on and off by an ignition switch. When the ignition switch is turned off, the engine, and also the circulation of lubrication fluid and coolant through the engine, stops. This subjects the engine and bearings to damage from overheating in the event the engine is at a high operating temperature when turned off.
This problem is particularly acute in turbo-charger equipped diesel or gasoline truck engines. When under heavy load, the turbo-chargers of such engine heat up substantially. Then, when the vehicle ignition switch is turned off, elevated temperatures within the turbo-charger may evaporate and break down lubricant within the turbo-charger bearings. This results in bearing failure and seizing up of the turbo-charger shaft and leads to expensive repairs and lost vehicle use.
In an attempt to address these problems, one prior art device has a timer for continuing the operation of a vehicle engine for a preset period of time after the vehicle ignition switch is turned off. As a result, coolant is circulated through the engine during this time, rather than stopping when the ignition switch is turned off. Although this approach does result in further cooling of the engine, there are a number of disadvantages to such devices.
For example, manufacturers of engines typically establish an optimum safe engine shut-off temperature. When an engine is shut off at or below this optimum temperature, the risk of damage to the engine and bearings of an engine turbocharger is minimal. With the prior art devices, under given operating conditions, the time set by the timer may be longer or shorter than necessary for the engine temperature to drop to a desired safe temperature level. If too long, unnecessary fuel is used and unnecessary engine wear is incurred because the engine operates longer than needed to cool it to a safe level. If the time is too short, the engine temperature may be above a safe level when the engine shuts off. Therefore, significant risk of damage to the engine is still present.
Therefore, a need exists for an apparatus, particularly applicable to vehicular engines having turbo-chargers, which continues to cool and lubricate the engine after the vehicle's ignition switch is shut off, which minimizes the risk of engine damage from overheating, and which minimizes engine wear and fuel usage.